Sophisticated Trojan loots business bank accounts

A German-speaking hacker crew is looting commercial bank accounts in four countries using a custom-built Trojan put in place by expertly crafted and extremely focused phishing attacks, a security researcher said Thursday.

The malware's most distinguishing feature, said Don Jackson, a senior security researcher at SecureWorks, is its ability to mimic the steps the human account owner would take to move money.

A variant of the Prg Banking malware, the new Trojan has stolen hundreds of thousands from accounts at some of the biggest banks in the US, the UK, Spain and Italy, said Jackson. "This is not widespread, but it is very dangerous. They've already stolen more than US$200,000 from the accounts we've monitored, but this has really flown under the radar."

Jackson also said he has found at least four servers that contain Prg configuration files and bogus versions of legitimate banking sites, as well as caches of data harvested by the Trojan.

The cleverness and technical know-how of the attackers was almost breathtaking. "If you were on the bank side of this connection [with the Trojan], it would appear to be a person on the other end running the account," Jackson said. "It would seem as if someone was clicking the keys on the virtual keyboard and sending wire transfers."

According to Jackson, the hackers -- who speak German, though they may not reside in Germany proper -- mined the vast amount of data collected previously by a less powerful generic version of Prg for evidence of commercial banking accounts, including specific URLs of offshore banks or indications of wire transfers.

The crew targeted commercial accounts, said Jackson, both because those accounts typically contain bigger balances and because they usually have the built-in ability to conduct wire transfers. Once they break into a business account, the hackers can quickly plunder it by using wire transfers to move its monies to hacker-controlled accounts.

With victim accounts picked, the hackers then create what Jackson called "very convincing" phishing e-mails and send them to the account owners, who have been identified using data stolen earlier. "They'll usually have the bank account number, and the first and last name of its owner," said Jackson, as well as security details, such as whether the account is protected by a one-time password. "The e-mail will claim that the user needs to download a new one-time password or soft token, but when the user clicks on the link and reaches the phish site, the Prg Trojan is downloaded instead."

From there, the highly automated account thief takes over. The malware alerts the hacker when the account owner is actually online with his bank, "piggybacking" on the session to silently steal the username and password without actually duping the user into entering it. Then using its ability to simulate keystrokes, the Trojan walks through all the steps a human being would take to, for instance, wire funds to another account. An account can be emptied in seconds.

"That's a very clever part of the Trojan," said Jackson. "How it downloads JavaScript from the command-and-control server so it looks like the [account owner] is accessing the account, not a bot." While less-sophisticated malware heads straight to a money transfer page without first appearing to "visit" the pages a real person would view before reaching the transfer page, Prg visits the bank's pages in order, as a person would. Because most antifraud looks for automated, nonhuman behavior, Prg won't trigger a fraud alert.

Each bank site has had customized code written for it, Jackson added, to make updating the Trojan-controlled PCs easier. If the hackers need to change the destination account -- because it's been spotted and frozen by local law enforcement, say -- a new one can be fed to the Trojans from the server.

"Fewer than 20 banks have been hit by this so far," said Jackson, "but they include some of the biggest banks in the US, UK, Spain and Italy.

He came close to praising the criminals. "To me, the automation of this is very, very crafty."

The surest defense against the Prg Trojan, Jackson concluded, is to be suspicious of any e-mail received from a bank. "Even if you recognize the sender, you should confirm that the sender sent that message before clicking on any links."

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